Fix chat sliding when the iPhone keyboard opens

Size the shell to the visible area while a field is focused, tuck the bottom bar away, and refit the chat as the keyboard comes and goes.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

public/shell.js

@@ -68,3 +68,22 @@
     else if (!e.shiftKey && (document.activeElement === last || !s.contains(document.activeElement))) { e.preventDefault(); first.focus(); }
   });
 })();
+
+// ---- iPhone keyboard: iOS shrinks only the visual viewport when the keyboard opens and pans the whole page to reveal the field, so the app used to slide up with it.
+// Pin the shell to what is really visible while typing and tuck the bottom bar away; chat and mail size themselves again on 'kbfit'.
+(function () {
+  const vv = window.visualViewport; if (!vv || !matchMedia('(pointer: coarse)').matches) return;
+  const root = document.documentElement; let raf = 0;
+  const typing = () => { const a = document.activeElement; return !!a && (a.tagName === 'TEXTAREA' || a.isContentEditable || (a.tagName === 'INPUT' && !/^(checkbox|radio|button|submit|reset|range|file|color|image)$/.test(a.type))); };
+  function apply() {
+    raf = 0;
+    const kb = typing() && window.innerHeight - vv.height > 120 && window.innerWidth < 768;
+    document.body.classList.toggle('kb', kb);
+    if (kb) { root.style.setProperty('--vvh', vv.height + 'px'); root.style.setProperty('--vvt', vv.offsetTop + 'px'); if (window.scrollY) window.scrollTo(0, 0); }
+    else { root.style.removeProperty('--vvh'); root.style.removeProperty('--vvt'); }
+    window.dispatchEvent(new Event('kbfit'));
+  }
+  const soon = () => { if (!raf) raf = requestAnimationFrame(apply); };
+  vv.addEventListener('resize', soon); vv.addEventListener('scroll', soon);
+  document.addEventListener('focusin', soon); document.addEventListener('focusout', () => setTimeout(soon, 80));
+})();